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handle src buffer underflow corner cases
[sdl_omap.git] / docs / html / sdlaudiocvt.html
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4>SDL_AudioCVT</TITLE
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68><HR
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70WIDTH="100%"></DIV
71><H1
72><A
73NAME="SDLAUDIOCVT"
74></A
75>SDL_AudioCVT</H1
76><DIV
77CLASS="REFNAMEDIV"
78><A
79NAME="AEN6884"
80></A
81><H2
82>Name</H2
83>SDL_AudioCVT&nbsp;--&nbsp;Audio Conversion Structure</DIV
84><DIV
85CLASS="REFSECT1"
86><A
87NAME="AEN6887"
88></A
89><H2
90>Structure Definition</H2
91><PRE
92CLASS="PROGRAMLISTING"
93>typedef struct{
94 int needed;
95 Uint16 src_format;
96 Uint16 dest_format;
97 double rate_incr;
98 Uint8 *buf;
99 int len;
100 int len_cvt;
101 int len_mult;
102 double len_ratio;
103 void (*filters[10])(struct SDL_AudioCVT *cvt, Uint16 format);
104 int filter_index;
105} SDL_AudioCVT;</PRE
106></DIV
107><DIV
108CLASS="REFSECT1"
109><A
110NAME="AEN6890"
111></A
112><H2
113>Structure Data</H2
114><DIV
115CLASS="INFORMALTABLE"
116><A
117NAME="AEN6892"
118></A
119><P
120></P
121><TABLE
122BORDER="0"
123CLASS="CALSTABLE"
124><TBODY
125><TR
126><TD
127ALIGN="LEFT"
128VALIGN="TOP"
129><TT
130CLASS="STRUCTFIELD"
131><I
132>needed</I
133></TT
134></TD
135><TD
136ALIGN="LEFT"
137VALIGN="TOP"
138>Set to one if the conversion is possible</TD
139></TR
140><TR
141><TD
142ALIGN="LEFT"
143VALIGN="TOP"
144><TT
145CLASS="STRUCTFIELD"
146><I
147>src_format</I
148></TT
149></TD
150><TD
151ALIGN="LEFT"
152VALIGN="TOP"
153>Audio format of the source</TD
154></TR
155><TR
156><TD
157ALIGN="LEFT"
158VALIGN="TOP"
159><TT
160CLASS="STRUCTFIELD"
161><I
162>dest_format</I
163></TT
164></TD
165><TD
166ALIGN="LEFT"
167VALIGN="TOP"
168>Audio format of the destination</TD
169></TR
170><TR
171><TD
172ALIGN="LEFT"
173VALIGN="TOP"
174><TT
175CLASS="STRUCTFIELD"
176><I
177>rate_incr</I
178></TT
179></TD
180><TD
181ALIGN="LEFT"
182VALIGN="TOP"
183>Rate conversion increment</TD
184></TR
185><TR
186><TD
187ALIGN="LEFT"
188VALIGN="TOP"
189><TT
190CLASS="STRUCTFIELD"
191><I
192>buf</I
193></TT
194></TD
195><TD
196ALIGN="LEFT"
197VALIGN="TOP"
198>Audio buffer</TD
199></TR
200><TR
201><TD
202ALIGN="LEFT"
203VALIGN="TOP"
204><TT
205CLASS="STRUCTFIELD"
206><I
207>len</I
208></TT
209></TD
210><TD
211ALIGN="LEFT"
212VALIGN="TOP"
213>Length of the original audio buffer in bytes</TD
214></TR
215><TR
216><TD
217ALIGN="LEFT"
218VALIGN="TOP"
219><TT
220CLASS="STRUCTFIELD"
221><I
222>len_cvt</I
223></TT
224></TD
225><TD
226ALIGN="LEFT"
227VALIGN="TOP"
228>Length of converted audio buffer in bytes (calculated)</TD
229></TR
230><TR
231><TD
232ALIGN="LEFT"
233VALIGN="TOP"
234><TT
235CLASS="STRUCTFIELD"
236><I
237>len_mult</I
238></TT
239></TD
240><TD
241ALIGN="LEFT"
242VALIGN="TOP"
243><TT
244CLASS="STRUCTFIELD"
245><I
246>buf</I
247></TT
248> must be <TT
249CLASS="STRUCTFIELD"
250><I
251>len</I
252></TT
253>*<TT
254CLASS="STRUCTFIELD"
255><I
256>len_mult</I
257></TT
258> bytes in size(calculated)</TD
259></TR
260><TR
261><TD
262ALIGN="LEFT"
263VALIGN="TOP"
264><TT
265CLASS="STRUCTFIELD"
266><I
267>len_ratio</I
268></TT
269></TD
270><TD
271ALIGN="LEFT"
272VALIGN="TOP"
273>Final audio size is <TT
274CLASS="STRUCTFIELD"
275><I
276>len</I
277></TT
278>*<TT
279CLASS="STRUCTFIELD"
280><I
281>len_ratio</I
282></TT
283></TD
284></TR
285><TR
286><TD
287ALIGN="LEFT"
288VALIGN="TOP"
289><TT
290CLASS="STRUCTFIELD"
291><I
292>filters[10](..)</I
293></TT
294></TD
295><TD
296ALIGN="LEFT"
297VALIGN="TOP"
298>Pointers to functions needed for this conversion</TD
299></TR
300><TR
301><TD
302ALIGN="LEFT"
303VALIGN="TOP"
304><TT
305CLASS="STRUCTFIELD"
306><I
307>filter_index</I
308></TT
309></TD
310><TD
311ALIGN="LEFT"
312VALIGN="TOP"
313>Current conversion function</TD
314></TR
315></TBODY
316></TABLE
317><P
318></P
319></DIV
320></DIV
321><DIV
322CLASS="REFSECT1"
323><A
324NAME="AEN6944"
325></A
326><H2
327>Description</H2
328><P
329>The <SPAN
330CLASS="STRUCTNAME"
331>SDL_AudioCVT</SPAN
332> is used to convert audio data between different formats. A <SPAN
333CLASS="STRUCTNAME"
334>SDL_AudioCVT</SPAN
335> structure is created with the <A
336HREF="sdlbuildaudiocvt.html"
337><TT
338CLASS="FUNCTION"
339>SDL_BuildAudioCVT</TT
340></A
341> function, while the actual conversion is done by the <A
342HREF="sdlconvertaudio.html"
343><TT
344CLASS="FUNCTION"
345>SDL_ConvertAudio</TT
346></A
347> function.</P
348><P
349>Many of the fields in the <SPAN
350CLASS="STRUCTNAME"
351>SDL_AudioCVT</SPAN
352> structure should be considered private and their function will not be discussed here.</P
353><P
354></P
355><DIV
356CLASS="VARIABLELIST"
357><DL
358><DT
359><SPAN
360CLASS="TYPE"
361>Uint8 *</SPAN
362><TT
363CLASS="STRUCTFIELD"
364><I
365>buf</I
366></TT
367></DT
368><DD
369><P
370>This points to the audio data that will be used in the conversion. It is both the source and the destination, which means the converted audio data overwrites the original data. It also means that the converted data may be larger than the original data (if you were converting from 8-bit to 16-bit, for instance), so you must ensure <TT
371CLASS="STRUCTFIELD"
372><I
373>buf</I
374></TT
375> is large enough. See below.</P
376></DD
377><DT
378><SPAN
379CLASS="TYPE"
380>int</SPAN
381> <TT
382CLASS="STRUCTFIELD"
383><I
384>len</I
385></TT
386></DT
387><DD
388><P
389>This is the length of the original audio data in bytes.</P
390></DD
391><DT
392><SPAN
393CLASS="TYPE"
394>int</SPAN
395> <TT
396CLASS="STRUCTFIELD"
397><I
398>len_mult</I
399></TT
400></DT
401><DD
402><P
403>As explained above, the audio buffer needs to be big enough to store the converted data, which may be bigger than the original audio data. The length of <TT
404CLASS="STRUCTFIELD"
405><I
406>buf</I
407></TT
408> should be <TT
409CLASS="STRUCTFIELD"
410><I
411>len</I
412></TT
413>*<TT
414CLASS="STRUCTFIELD"
415><I
416>len_mult</I
417></TT
418>.</P
419></DD
420><DT
421><SPAN
422CLASS="TYPE"
423>double</SPAN
424> <TT
425CLASS="STRUCTFIELD"
426><I
427>len_ratio</I
428></TT
429></DT
430><DD
431><P
432>When you have finished converting your audio data, you need to know how much of your audio buffer is valid. <TT
433CLASS="STRUCTFIELD"
434><I
435>len</I
436></TT
437>*<TT
438CLASS="STRUCTFIELD"
439><I
440>len_ratio</I
441></TT
442> is the size of the converted audio data in bytes. This is very similar to <TT
443CLASS="STRUCTFIELD"
444><I
445>len_mult</I
446></TT
447>, however when the convert audio data is shorter than the original <TT
448CLASS="STRUCTFIELD"
449><I
450>len_mult</I
451></TT
452> would be 1. <TT
453CLASS="STRUCTFIELD"
454><I
455>len_ratio</I
456></TT
457>, on the other hand, would be a fractional number between 0 and 1.</P
458></DD
459></DL
460></DIV
461></DIV
462><DIV
463CLASS="REFSECT1"
464><A
465NAME="AEN6989"
466></A
467><H2
468>See Also</H2
469><P
470><A
471HREF="sdlbuildaudiocvt.html"
472><TT
473CLASS="FUNCTION"
474>SDL_BuildAudioCVT</TT
475></A
476>,
477<A
478HREF="sdlconvertaudio.html"
479><TT
480CLASS="FUNCTION"
481>SDL_ConvertAudio</TT
482></A
483>,
484<A
485HREF="sdlaudiospec.html"
486><SPAN
487CLASS="STRUCTNAME"
488>SDL_AudioSpec</SPAN
489></A
490></P
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SDL with some OMAP hardware support